For farmers that follow sustainable and organic farming methods, cover cropping is a common
practice, with many great ecological benefits.
Cover crops can literally cover the soil, serving as a mulch whether living or dead. They can also
be incorporated into the soil as either a nitrogenous “green” manure, or as more mature,
carbonaceous addition. Including cover crops in your rotation will
improve soil fertility and tilth by
adding organic matter (which
also
increases
the water-holding capacity of your soil),
breaking up clods, and
fracturing
compaction from tillage. Cover crops
prevent erosion,
suppress weeds, and
provide
habitat for beneficial insects, and allow you to
fix (or add)
nitrogen and
mine or
scavenge nutrients for your next cash crop. Some cover crops can double as
cash crops or forage for livestock.
There are a wide variety of cover crops out there, all of which provide at least a couple of the
benefits listed above. Any cover crop you can work into your crop planning is generally better than
none at all, and jumping in with whatever your neighbors or trusted fellow farmers are using isn’t a
bad place to start. But by putting careful consideration into which cover crops you use, you can
target and maximize your benefits, and really put that cover crop to work for your farms’ specific
needs.
Here are some questions to consider when choosing a cover crop or cover crop mix:
What do I most want my cover crop to accomplish?
Primary goals could be the prevention of erosion, scavenging or fixing of nitrogen, suppression of
weeds, or improving soil tilth. Which one or two of these are most important, and for which
fields?
What are the windows in my cash crop schedule where I could work in cover crops?
When do you anticipate harvesting your cash crops, and when you anticipate those fields to be
available for a cover crop? Consider also when and what you plan to plant there the following
season, and what that means for you in terms of being able to get into the fields to incorporate or
mow, especially if a wet spring could be a limiting factor.
Are there any other considerations, requirements or limitations to consider?
If you are growing in an area that suffers from drought, you might look for a crop that does not
require summer water. Or, the type of equipment you have access to might limit your ability to mow
or incorporate more carbonaceous, mature cover crop. If you are growing strips of cover crop
alongside cash crops, consider height and shading, and the timing for the incorporation of your
cover crop with the harvest of your cash crop.
Identifying your primary goals and your window(s) will significantly narrow your options for the
best cover crops.
For example, let’s say you are growing in an area with dry summers and heavy winter rains, and your
number one struggle is with nutrient losses and poor soil quality caused by erosion. In this case,
one of your primary goals may be to establish a dense stand of cover crop in the fall, before
winter rains set in, to minimize erosion. A secondary goal may be to add organic matter to improve
your soil’s ability to retain water.
There are many crops that are excellent at both preventing erosion and adding organic matter,
including annual ryegrass, sorghum-sudangrass, cereal rye and barley to a variety of legumes from
cowpeas to clover. To significantly narrow this long list of potentially appropriate cover crops,
consider your field schedule.
Your window for cover cropping opens following a harvest of spring broccoli. This leaves you
with a lot of options, from erosion-controlling crops that can be seeded in the heat of summer, like
a sorghum-sudangrass hybrid, to anything that can be sown in the cooler temperatures of fall, such
as an annual ryegrass, oats or barley. Because you’ll be following broccoli, you may want to stay
away from brassicas for pest reasons.
If you have a long window, and won’t be planting into the field until early summer, you may opt for
something that can overwinter and provide a burst of biomass in the spring. A combination of rye and
hairy vetch would give you vigorous spring growth, serving as a green manure for your early summer
crop and accomplishing your secondary goal of adding organic matter. If, however, your window closes
early (perhaps you’ll be planting an early spring crop the following season, and will need to get
into the fields quickly), you may want to go with something like the frost-sensitive
sorghum-sudangrass or oats, which will winterkill in lower hardiness zones – something that won’t
get away from you in the spring.
Are there any other factors to consider? How well can the cover crops you’re thinking about
using establish themselves in the drier months before the rains come? Do you have the water to
irrigate them in? Sorghum-sudangrass is very drought tolerant, whereas annual ryegrass is not (but
is tolerant of excessive moisture). Perhaps the best option is to plant the sorghum-sudangrass
immediately following your spring brassica crop to capture the soil moisture, scavenge nitrogen and
improve your soil structure, then till it in and plant the annual ryegrass/vetch mix later in the
fall. (As an added benefit, hairy vetch attracts beneficials such as predatory and parasitoid wasps
and lady beetles.)
For more on selecting the best crops for your farm, I highly recommend
Managing Cover Crops Profitably: an excellent and comprehensive resource
available for free online on the Sustainable Agriculture Research and Education (SARE) website. In
selecting a list of suitable crops to meet your needs, you may find it helpful to consult a cover
crop comparison chart. Charts are available online from sources such as
Peaceful
Valley and
Johnny’s Selected Seeds. For more detail on some of these crops, check
out the
plant guides offered by the NRCS. For regionally-specific resources
(such as this one for growers in
Oregon and Washington), look to your local seed suppliers, ag extension
offices, or simply to any neighboring farmers growing comparable crops.
LINKS / RESOURCES
Managing Cover Crop Profitably (SARE)
The comprehensive manual on cover cropping from the Sustainable Agriculture Network, complete with
helpful charts of top regional cover crop species, an overview of legume and non-legume cover crops,
and profiles of specific crops.
Cover Crops and Soil Health (NRCS): Cover Crop Plant Guides
A series of plant guides to describe the characteristics of eleven of the most commonly used cover
crops.
Crop Plant Guides
Cover Crop Resources and Seed Vendors for Oregon and Washington (USDA/NRCS):
A guide to regional and national sources for cover crop seed vendors and a diverse list of cover
crop-related resources.
Johnny’s Selected Seeds: Farm Seed Comparison Chart
Peaceful Valley: Cover Crop Comparison Chart
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After graduating from UCSC's
Center for Agroecology and Sustainable Food Systems, Lauren Alexandra Kaplan spent a season at
an organic CSA farm in California before returning east to farm in the Hudson Valley. Prior to
pursuing farming full time, she worked in book publishing and helped to launch an urban farm in
NYC. Alexandra is an avid salsa dancer and maker of jams, pickles, and kraut.
lou desena
Dec 5, 2016 at 4:11 PM
enjoy you information and resources-
Bunny Goodwin
Dec 7, 2016 at 5:38 PM
What cover crops do you recommend for raised beds in a school garden?
Lauren
Dec 19, 2016 at 5:10 PM
Hi Bunny! Buckwheat is a nice summer cover crop with a quick turn-around time, and easy to incorporate into the soil. If you an do any cover cropping during the school season, try planting a grass and a legume together for a winter cover crop, and incorporating with students in the spring.